The present invention is directed to an improved hydraulic cement and to a hydraulic cement composition having therein the subject improved cement. Specifically, the present invention relates to an improved hydraulic cement composed of a mixture of an imidized acrylic polymer, as fully described below, and hydraulic cement and to hydraulic cement compositions such as mortars and concrete which is capable of imparting high flowability to said compositions and of causing the treated composition to retain high flowability over a sustained period of time without imparting a significant delay in the initial set time for the composition.
Although increased flowability can be attained by using large dosages of water in a hydrating cement composition, it is well known that the resultant cement based structure will have poor compressive strength and related properties. Various additives have been proposed to increase the flowability (known as "slump") to cement composition, such as mortar and concrete compositions, without increasing the water content of the initially formed composition. Such additives have been classified as "cement superplasticizers" and include, for example, compounds, such as naphthalene sulfonate-formaldehyde condensates lignin sulfonates and the like.
More recently, copolymers of alkenyl ethers and acrylic acid or maleic anhydride, and derivatives thereof, have been proposed as agents suitable to enhance slump [Japanese Patent Publication (Kokai) Nos 285140/88 and 163108/90]. Further, copolymers formed from the copolymerization of hydroxy-terminated allyether and maleic anhydride or the allyether and a salt, ester or amide derivative of maleic anhydride such as disclosed in U.S. Pat. No. 4,471,100 have been proposed as cement admixtures capable of enhancing slump.
In each of the above instances, the proposed cement admixture material when used in a cement composition does not provide the desired combination of properties or only provide them in low degrees. For example, esterified acrylate copolymers, while providing good slump enhancement, also causes the treated cement composition to exhibit excessive set retardation.
It is highly desired to have an admixture for cement compositions which is capable of imparting to the treated composition, a high degree of slump, of preventing a decrease in slump (decrease in flowability) over a sustained period of time, and at the same time, not causing the composition to exhibit excessive set retardation.